The index student, studying at a Japanese language school in 2015, developed symptoms of TB in September and was diagnosed via chest X-ray in November. However, the student, unaware of the seriousness of his illness, continued attending classes after symptoms appeared.

Tokyo has reported a rise in TB cases in recent years.

Tuberculosis is caused by a bacterium called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain. If not treated properly, TB disease can be fatal.

TB is spread through the air from one person to another. The TB bacteria are put into the air when a person with TB disease of the lungs or throat coughs, sneezes, speaks, or sings. People nearby may breathe in these bacteria and become infected.

People who breathe air containing the TB bacteria may become infected. People infected with TB bacteria have a lifetime risk of falling ill with TB of about 10%. Symptoms of active TB include cough, fever, night sweats, and unexplained weight loss. Active TB disease is usually curable with a standard 6-month course of antibiotic drugs.

According to health officials, the index student has finished his treatment and his condition has improved.

Tokyo health official, Yoshiyuki Sugishita said, “There is no ongoing risk of further transmission from those already diagnosed with infections as they have already had treatment.”